Field of the Invention
This disclosure relates to a sheet conveyance apparatus conveying sheets.
Description of the Related Art
Hitherto, an image forming apparatus such as a copier, a printer, or a facsimile is provided with a sheet conveyance apparatus conveying sheets. The sheet conveyance apparatus conveys a sheet to an image forming portion, and a toner image formed on a photoconductive drum is transferred onto the sheet. The sheet onto which the toner image has been transferred is conveyed to a fixing portion and is then conveyed to a discharging portion. In recent years, in an image forming apparatus, there has been an increasing demand for further improvement in productivity, that is, improvement in the number of sheets on which images are formed per unit time.
For this reason, a sheet conveying speed has been attempted to be increased, or an interval (hereinafter, referred to as a sheet interval) from a rear end of a continuously conveyed sheet to a front end of the next sheet has been attempted to be reduced. It is noted that, in an image reading apparatus reading an image formed on a sheet (document) by using an image reading portion, a sheet interval has been attempted to be reduced.
Meanwhile, in a certain conventional sheet conveyance apparatus, when a sheet is conveyed, switching operations in various switch members, an operation of switching a direction of rotation of a sheet conveying portion, or the like is performed on the basis of detection of a sheet front end. In order to detect a front end of a sheet, a sheet detection portion detecting a front end of a sheet is provided on a sheet conveyance path.
Here, as the sheet detection portion, there is one including an abutting member which abuts on a front end of a sheet and pivots, and a detection sensor which detects the pivoting abutting member and outputs a detection signal to a control portion. In such a sheet detection portion, if the abutting member pressed by a sheet is moved (changed) from a non-detection position (non-detection state) to a detection position (detection state) where the detection sensor can perform detection, the detection sensor detecting the movement outputs a detection signal to the control portion.
If the detection signal is input, the control portion determines that the conveyed sheet has reached the sheet conveyance path. Thereafter, if the sheet passes through the abutting member, and the abutting member returns from the detection position to the original non-detection position as a result of the pressing from the sheet being released, a detection signal is not output from the detection sensor, and thus the detection signal is not input to the control portion any longer. Thus, the control portion determines that the sheet has passed through the sheet conveyance path.
However, in the case where the sheet detection portion has such a configuration, since some time is required for the abutting member to return from the detection position to the non-detection position, passage of a sheet cannot be detected if a sheet interval is shortened.
Therefore, JP-A-2008-1465 discloses a sheet conveyance apparatus in which a pivotal shaft of an abutting member is obliquely inclined with respect to a direction of sheet conveyance when viewed from a normal direction of a sheet surface. As a result of the pivotal shaft of the abutting member being obliquely inclined, a falling amount of the sensor in the direction of sheet conveyance is reduced during passage of the sheet, that is, when the sensor starts operation, and thus it is possible to reduce a mechanical loss until the abutting member returns from the detection position to the non-detection position.
JP-A-2012-144350 discloses a sheet conveyance apparatus using a method in which an abutting member returns from a detection position to a non-detection position through rotation thereof instead of a method in which the abutting member is reciprocally moved between the detection position and the non-detection position. It is possible to considerably reduce a mechanical loss by rotating the abutting member once whenever a sheet passes. In the certain conventional sheet conveyance apparatuses, for example, in the case where the pivotal shaft of the abutting member is disposed so as to be obliquely inclined with respect to the direction of sheet conveyance when viewed from the normal direction of a sheet surface, the abutting member starts to return to the non-detection position after a rear end of a sheet passes.
In other words, the abutting member cannot start an operation of returning to the non-detection position before the rear end of the sheet passes. For this reason, even in a case where the abutting member is inclined, a shorter sheet interval cannot be handled. In the case where the abutting member is rotated once whenever a sheet passes, the number of components increases, and a space for rotating the abutting member in the direction of sheet conveyance is necessary. Thus, a size thereof becomes large, and cost increases.